This paper outlines and demonstrates a strategy for coupling of integrated hydrologic model and Geographic Information System (GIS) to meet pre/post processing of data and visualization. Physically based fully distributed integrated hydrologic models seek to simulate hydrologic state variables and their interactions in space and time. The process requires interaction with a range of heterogeneous data layers such as topography, soils, hydrogeology, climate, and land use. Clearly, this requires a strategy for defining topology definitions, data gathering and development. Traditionally GIS has been used for data management, analysis and visualization. Integrated use and streamlineed development of sophisticated numerical models and commercial Geographic Information Systems (GISs) poses challenges inherited from proprietary data structures, rigidity in their data-models, non-dynamic data interaction with pluggable software components and platform dependence. Independent hydrologic modeling systems (HMSs), GISs and Decision Support Systems (DSSs) not only increase model setup and analysis time but they also result in data isolation, data integrity problems and broken data flows between models and the tools used to analyze their inputs and results. In this paper we present an open-source, extensible and pluggable architecture, platform independent "tightly- coupled" GIS interface to Penn State Integrated Hydrologic Model (PIHM) called PIHMgis. The tightcoupling between the GIS and the model is achieved by the development of PIHMgis shared-data model to promote minimum data redundancy and optimal retrievability [Kumar et al., 2008]. The procedural framework of PIHMgis is demonstrated through its application to Shaver's Creek Watershed located in Susquehanna River Basin in Pennsylvania.